Directive antenna system



Aug. 15, 1950. c. c.- CUTLER DIRECTIVE ANTENNA SYSTEM 2 Sheets-Sheet 1 Filed July 21, 1945 BANDW/DTH CHARACTEkUT/C FOR ENTIRE ANTENNA SYSTEM Qw AMwQ WAVELENGTH IN CENT/METERS lNl ENTOR C C. CUTLER ATTORNEY Aug. 15, 1950 c. c. CUTLER DIRECTIVE ANTENNA SYSTEM 2 Sheets-Sheet 2 Filed July 21 1945 DIRECTIVE Pure-m: or

PR/MARY ANTENNA RELATIVE FIELD STRENGTH- DEC/EELS FIG, 6

DIRECTIVE PA T'TERNS OF ENTIRE SYSTEM H-PL ANE E -PLANE GAIN J05 DEC/EELS RELATIVE FIELD J'TRENGTHDECIBELS INVENTOR By C C. CUTLER ATTORNEY Patented Aug. 1 5,1950

DIRECTIVE ANTENNA SYSTEM Cassius C. Cutler, Oakhurst, N. J assignor to Bell 7 Y Telephone, Laboratories, Incorporated, New

a York, N. Y., a corporation 01' New York Application July 21, 1945, Serial No. 606,427

- This invention relates to antenna systems and particularly to microwave directive antenna systemsr .rwAs is well known, antenna systems .c omprising a parabolic reflector and a primary antenna of the front or rear feed dielectricflguide type .are widely used in microwave radar systems and microwave communication systems. "While, for certain installations, the rear-feed type is preferred, the front-feed type may be employed with advantage in certain other installations. Also, as is known, front-feed and rear-feed parabolic systems have .been suggested for'securing a J point beam or a fan beam. :Thus, Patent 2,434,253 granted to A. C. Beck on January 13, 1948 and the copending application of (7.3. H. 'Feldman, Serial No, 489,740,,filed June 5, 1943, now Patent No. 2,482,162, issued September 20, 1949, disclose point-beam systems comprising a fanebeam. cylindrical-parabolic reflector and a front-feed fan-beam primary antenna,"and Patent 2,409,183 granted to A. C. Beck on October 15, 1946 discloses a fan-beam lobe-switching systemcomprising a fan-beam paraboloidal re -flector and a front-feed point-beamprimary am tenna; -My Patent 2,422,184 granted'on June 17, 19.4.7 and my application, serial 'No. 546,687, filed July 26, 1944, now Patent No. 2,483,575, issued October 4, 1949, disclose point-beam systems comprising a point-beam paraboioidal re- 5 flector and a rear-feed dual-hornxpoint-beam primary antenna, and the last-mentioned "application also discloses a fan-beam'system com- ,prising'a fan-beam paraboloidal reflector and a rear-feed fan-beam dual-horn primary antenna. :In general, the point-beam antennas areemployed in radar systems in which target detection or target direction finding, inboth the azi- .muthal and elevational scanning planes, 'is' desired; and fan-beam antennas are utilized in radar systems in which target detection or direction finding in only one scanning plane is required. While highly satisfactory results have been:obtainedwith the antenna'systems mentioned above, and while the above-mentioned front-feed systems have been usedgwith success, it now appears desirable to secure a fan-beam antenna system comprising a frontfeed primary antenna and having distinct advantages over the front-feed fan-beam systems otthe-prior art. It is one object of this invention to secure, in a front-feed parabolic antenna system, optimum illumination of the reflector.

It is another object of this invention to obtain,

in a front-feed primary antenna system, a fana 3-Claims. (c1. 250'33.63)

2 beam major lobe of optimum shape for illuminating a fan-beam paraboloidal reflector. I It is another object of this invention to secure a highly efficient, high gain, fan-beam'antenna system having a wide bandwidth characteristic. It is another object of this invention to "see, cure, in a high gain microwave antenna system, a directive characteristic including a fan-beam major lobe and negligible minor lobes, utilizlngia paraboloidal reflector "and a front-.feed dielectric guide primary antenna.

It is another object of this invention to secure, in a fan-beam system comprising a movable paraboloidal reflector and a stationary frontfeed primary antenna, a directive pattern which remains substantially constant in shape as the reflector axis is moved or tilted relative to its normal horizontal position.

As used herein, the term parabolic reflecto generically applies to a cylindrical parabolic reflector and a paraboloidal reflector and the term focus generically applies to focal point and focal line; The term wave guide applies to conventional conductive :lines, for example, a coaxial line, and to dielectric guides such as a metallic tube filled with the air dielectric or a solid dielectric. The term air wavelength refers to the wavelength as measured in free space, that is, the air medium outside of the guide; and the term guide wavelength refers to the wavelength as measured in the dielectric medium forming the guide. The termffdirective characteristic refers to the three dimensional or solid directive diagram and the term directive pattern refers to the trace of the directive characteristic on a given plane. The term beam refers to the major lobe in .a given receiving or transmitting pattern, and the terms E-plane and H-plane refer, respectively, to the plane of electric polarization and the-plane'of magnetic polarization, of the waves utilized. j

In accordance with one embodiment of -.the invention, a front-feed dual horn primary antenna is associated with a rectangular or quasielliptical paraboloid.- The dual-horn antenna-is attached to a rectangular dielectric guide and positioned at the reflector focus; The guide ex tends vertically in front of the lower half portion of the reflector and is connected at itsnear end to a radartransceiver. The 'E-plane of the waves utilized is horizontal.-- A pairof rectangular openings or irises spaced vertically a guide wave,- lengthapart are provided at the far end of the vertical guide wall facing the reflector; and these irises: constitute the throat apertures :of; the two horns, or horn-like guides, comprising the dual horn antenna. The horn mouth apertures are vertically spaced approximately an air wavelength apart and each aperture illuminates, or receives energy from, the entire reflector. The major lobe of the dual horn antenna has a fanbeam shape, the wide beam dimension being horizontal; and the kf'an-be'ams of the dual horn primary antenna and of "the reflector are perpendicularly related. The gain of the combined system is relatively high. The dimensions of the mouth and throat apertures are critically .chosen so that the reflector illumination is graded from a maximum at the vertex to :a smallfvalueat the reflector periphery, whereby the minor lobes in the directive characteristic of the "whole system have negligible intensities.

The invention will be more fully understood from a perusal of the following specification taken in conjunction with the drawing on which like-reference characteristics idenote relements :ef similar function :and on which:

.Fig. 1 fisaperspective view pf-pneembndiment oithe invention;

.:;Figs. 2, ,3 Land A are, respectively, ifront, :side and .top views-of the iront feed primary antenna included in the embodiment of *Fig. :1; fi iFig. 5 :illustrates the measured =E-1plane -:and H -j'plane directive patterns for the primary ran-- tenna included in the embodiment of Fig. '1;

Fig. 6 illustrates the measured 'Eaplane and H-plane directive ipatterns for the 'complete system .of Fig. 1;:and,

Fig. 7' illustrates the measured bandwidth characteristic of the "embodiment :of :Fig. 2-1.

' Referring to Figs. 1, '2, 3 and '4, reference numeral 1 denotes a quasi-elliptical lparaboloida'l reflector having a focal pointZ, :anaxis 3, aslatus rectum 4 and *a vertex '5. "The quasi-ellipticalreflector, considered alone, is disclosed and claimed in my copending application .Serial No. 5463.687 mentioned above. The projectionoiit-he periphery :ofathe reflector'on "the plane perpendicular to axis3 and including the latus :rectum *4 '18 ran ellipses. In Fig. 1, the axis 3 and thelatus -rectum plane containing the ellipse 6 and focal point 2, are horizontal 'and vertical, respectively.

Reference numeral 1:denotes atilting mechanism comprising a gear or cam box 8 and-a red 9 attached to the vertex '5 of reflector l and-associated with the box '8. The mechanism :l unay be utilized, if desired, for the purpose of manually or automatically tilting reflector l :downwardly so that its axis is aligned, for example, with a direction 1"!) making an angle "with "the horizontal position o'f'axis 3.

Reference numeral 11 denotes :a translation device, such as a radar transceiver, and numeral lZ-designates a rectangular dielectric guide con-'- nected at its near end to device 1. The guide 12 comprises two wide metallic side walls 13, M, a

rear narrow wall 15 facing the reflector, a front narrow wall IG'I'a top horizontal end wall W, a top inclined end wall l'8 and the-air dielectric l9. Numeral 20 denotes an adjustable tuning plug inserted in the top end wall H. "The guide [2 extends vertically in front of the lower half portion of reflector I and perpendicular to the long dimension of the elongated reflector l.

Near the top of guide l2 two rectangular irism 2! are provided in the rear narrow wall 15, the centers of the irises being spaced vertically, and along the longitudinal dimension of guide I 2, a guide wavelength Ag apart.

Numeral 22 designates adual horn'primar-ynnthese apertures being spaced vertically,

4 tenna or head attached to guide 12 and comprising two short air-filled dielectric guides 23. The rectangular guides 23 are electrically open at both ends and comprise two vertical metallic side walls 24, the top metallic wall 25, the bottom metallic wall 26 and the common center metallic wall or partition 21. The wall 2'! is pf sheet metal and has a'tnegligible thickness.

Numerals!!! denote the-rectangular mouth apertures of the horn-like guides 23, the centers of and therefore along the short dimension of the elongated reflector l, and air wavelength, la, apart.

dimensions of the mouth and throat apertures are substantially equal, whereas the longitudinal vertical dimension of the mouth aperture is greater than the corresponding dimension of the throat aperture. Numeral 29 denotes a thin mica :window which covers the :two mouth .apertures 28 and which, together with the aperture'd rubber gasket 30, is included between the :two brass plates 3 I. The window'assembly 29,13fland 3| is fitted to'the mouth'end of the dual horn antenna 22 and is securely held together 'by means of "the bolts 32. 1

In operation, horizontally polarized microwaves :supplied by the transmitter in the transceiver H are'conveyed over guide .12 to the "two horn-like guides 23 and emitted'towardreflector 'l by the two antenna apertures 28. Assuming the reflector axis is horizontal, "the wavelets impinging upon the reflector l are redirected aali'nrg the "general direction of the axis .3. Morespecif- .ically, the wave components arriving in guide it! at the-irises 2! are .cophasal sincethe :irises are {a guide wavelength apart, and the wave components projected into space 'by the mouth :aper- ..tures are also cophasal, :since the mouth apertures are an air wavelength apart. fI-Ience the two horn-like guides constitute a two element broadside array, the direction of "greatest radio action of the array :being perpendicular to :t-he vertical array axis and aligned with '-the Ehori- 'zontal reflector axis 3. In reception :the converse operationrobtains :byreason of 'the:reciprocity theorem.

Referring to Fig. 5, reference numerals :33 and 3:! denote, respectively, the measured H plane and E-plane directive patterns of the dual-horn primary antenna'22,xobtained at a designer mean guide wavelength kg equal 'to 3.2 centimeters. The H-plane pattern includes the major lobe 35, the null or dip 36 and the minor lobe .31 :and the -E-plane pattern includes, in the iQD :degree angular range, only the maiorilobe :38. :At the half power point 39, three decibels :down from the peak value, the widths of the :H 41513118 and E-plane major lobe patterns are, respectively, about '30 andi degrees. Hence, the primary antenna 22 produces .a horizontal fan-beam, the wide and narrow beam dimensions being parallel to the long and short dimensions of the :quasielliptical reflector l.

In additionjbyreasonof the critical dimensions ofthe throat "and mouth apertures 28., 21 of the dual-horn antenna, the contours of the fan-beam in the E and H planes are such'that the taper or variation in the illumination of a'reflector having a focal length of 815m, a long or =ma'jor axis dimension of 23.0w and a short or minor axis dimension of 8.0m, "is the optimum. Thus, the illumination at the vertex is a maximum, whereas at the periphery it is about 10 decibels below maximumthat is, negligible. In other words, only the portion of the fan-beam shown above the -10 decibel point, denoted by reference line 50, is effective in illuminating the elongated reflector I. The minor lobe 37, it will be noted, is about 11.5 decibels down and therefore of small consequence in so far as the illumination of reflector l is concerned. In the tested system, the transverse dimensions of the throat and mouth apertures 2 l, 28 was about 0.27m and the longitudinal dimensions of the throat and mouth apertures were about 0.5)g and 0.72m. The wide transverse dimension of guide 12 was 0.64m.

Referring to Fig. 6, reference numerals 4i and 42 denote the measured E-plane and H-plane patterns of the combined system comprising reflector l and the primary antenna 22, taken at the mean wavelength Ag equal to 3.2 centimeters. The H-plane pattern 41 includes a major lobe t3, the dips 4 and the first minor lobes t5, and the E-plane pattern includes the major lobe 16, the first nulls 4'1, the first minor lobes t6, the second nulls 49 and the higher order minor lobes 50 and 5|. The half power widths of the H-plane and E-plane major lobe patterns, are, respectively,

- 8.0 and 2.6 degrees, 50 that the system i, 22 has a vertical fan-beam perpendicularly related to the fan-beam of the primary antenna 22. The measured gain of the system is about 30.5 decibels, as measured along the reflector axis 3.

The curve 52, Fig.7, illustrates the measured bandwidth characteristic of the complete system, taken over the 3.17-3.23 centimeter bands. As shown by this curve, the complete antenna system I, 22 is substantially matched to the main guide 12 over the band and, in the central portion of the band, the characteristic is relatively flat, as is desired.

The antenna system I, 22 described above is especially suitable for use in an aircraft radar employed for azimuthal scanning and for scanning the ground target plane. As previously indicated the reflector I may be tilted downwardl for the purpose of scanning the earths surface in front of and below the aircraft. When the reflector is tilted relative to the primary antenna, the measured gain decreases nearl linearly as the tilt angle, 0, increases and at -25 degrees tilt the gain is about 2 decibels below the gain obtained with the axis 3 horizontal. At the 25 degree tilt angle, the beam deflection is 43 degrees. Also, the E-plane pattern remains fairly constant in shape as the reflector I is tilted or moved from the zero degree position down to, for example, the 25 degree position.

Thus, in accordance with the invention, a frontfeed dual-horn primary antenna is provided for securing optimum illumination of an elongated reflector whereby, in a quasi-elliptical paraboloidal antenna system, a high gain and a highly useful fan-beam are obtained.

- Although the invention has been explained in connection with a specific embodiment, it is to be understood that it is not to be limited to the embodiment described inasmuch as other apparatus may be employed in success-fully practicing the invention.

What is claimed is:

1. In combination, a main air-filled dielectric guide connected to a translation device and having a metallic longitudinal Wall, a pair of parallel dielectric horn guides having coplanar nonsquare rectangular mouth apertures and coplanar non-square rectangular throat apertures, the centers of said mouth apertures :being spaced an air wavelength apart, said throat apertures being located in said wall and the centers of said throat apertures being spaced longitudinally a guide wavelength apart, said air and guide wavelengths being substantially diiferent, and said mouth and throat apertures having substantially different long dimensions.

2. A broadside microwave antenna arra comprising a main dielectric guide having in one longitudinal wall a pair of non-square rectangular irises, a pair of dielectric horn guides attached to said main guide and having coplanar non-square rectangular mouth apertures, said irises constituting the throat apertures of said horn guides, the centers of said irises being spaced farther apart than the centers of said mouth apertures, the long dimension of each iris being one-half a guide Wavelength and the long dimension of .each mouth aperture being approximately an air wavelength, an air wavelength being equal to 0.72 guide wavelength, and a translation device co11- nected to said main guide.

3. A broadside microwave antenna array comprising a pair of dielectric horn guides having parallel axes and coplanar rectangular mouth apertures, each of said apertures having a long dimension equal to 0.72 guide wavelength, a main dielectric guide extending perpendicular to said axes and having in one longitudinal wall a pair of longitudinally spaced rectangular irises constituting the throat apertures of said horn guides, each of said irises having a long dimension equal to 0.5 guide wavelength, the centers of said irises being farther apart than the centers of said mouth apertures, and a translation device connected to said main guide.

CASSIUS C. CUTLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,973,206 Schroter Sept. 11, 1934 2,095,083 Renatus Oct. 5, 1937 2,206,923 Southworth July 9, 1940 2,283,935 King May 26, 1942 2,287,533 Peterson June 23, 1942 2,409,183 Beck Oct. 15, 1946 2,436,380 Cutler Feb. 24, 1948 OTHER REFERENCES Fundamentals of Electric Waves by H. H. Skilling, John Wiley 8: Sons, New York (1942) 

